Noise cancelling microphone apparatus

ABSTRACT

Example embodiments include a method of reducing noise include forming a main signal and one or more reference signals at a beam-former based on at least two received audio signals, detecting voice activity at a voice activity detector, where the voice activity detector receives the main and reference signals and outputting a desired voice activity signal, adaptively cancelling noise at an adaptive noise canceller, where the adaptive noise canceller receives the main, reference, and desired voice activity signals and outputs an adaptive noise cancellation signal, and reducing noise at a noise reducer receiving the desired voice activity and adaptive noise cancellation signals and outputting a desired speech signal.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/181,059, filed Feb. 14, 2014, which claims the benefit of U.S.Provisional Application No. 61/780,108, filed on Mar. 13, 2013. U.S.application Ser. No. 14/181,059 also claims the benefit of U.S.Provisional Application No. 61/839,211, filed on Jun. 25, 2013. U.S.application Ser. No. 14/181,059 also claims the benefit of U.S.Provisional Application No. 61/839,227, filed on Jun. 25, 2013. U.S.application Ser. No. 14/181,059 also claims the benefit of U.S.Provisional Application No. 61/912,844, filed on Dec. 6, 2013.

U.S. application Ser. No. 14/181,059 was co-filed on the same day, Feb.14, 2014, with “Eye Glasses With Microphone Array” by Dashen Fan, U.S.application Ser. No. 14/180,994. U.S. application Ser. No. 14/181,059was co-filed on the same day, Feb. 14, 2014, with “Sound Induction EarSpeaker For Eye Glasses” by Dashen Fan, U.S. application Ser. No.14/180,986. U.S. application Ser. No. 14/181,059 was co-filed on thesame day, Feb. 14, 2014, with “Eyewear Spectacle With Audio Speaker InThe Temple” by Kenny Chow et al., U.S. application Ser. No. 14/181,037.

The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

In many computer and electronic systems that record sound, it isdesirable to reduce background noise. Reducing background noise canprovide advantages to the user such as outputting a clearer audiosignal. Reducing background noise can also provide advantages toprocesses such as automatic speech recognition.

The acoustic characteristics of a noise canceling close-talk microphoneare often very useful. Such microphones (also referred to herein as“mics”) often have a long boom form factor, which positions themicrophone in front of the user's mouth. However, such a form factor hasdrawbacks, including deteriorated performance due to ongoing moisturefrom the user's mouth accumulating on the surface of the microphonemembrane (ECM microphone) and a form-factor considered inconvenient andannoying by most users.

Therefore, there is a need for a noise cancelling microphone apparatusand method of its use that overcomes or minimizes the above-referencedproblems.

SUMMARY OF THE INVENTION

More specifically, some embodiments include shortening the boom, movingthe microphone away from the user's mouth, using acoustic housings suchas polymeric or rubber extensions or boots to extend the acoustic portsof the microphones, therefore extending the effective close talk rangewhile maintaining the noise canceling property for faraway noises.

Example embodiments of the present invention include a short boomheadset, such as an audio headset for telephony suitable for enterprisecall centers, industrial, and general mobile usage, an in-line “earbuds” headset with an input line (wire, cable, or other connector),mounted on or within the frame of eyeglasses, a near-to-eye (NTE)headset display or headset computing device, a long boom headset forvery noisy environments, such as industry, military, and aviationapplications, and a gooseneck desktop-style microphone, which can beused to provide theater or symphony-hall type quality acoustics withoutthe structural costs.

Example embodiments as well as further details and benefits of thepresent invention are presented in more detail following the claims.Features of the invention presented herein which are couple may bephysically and/or communicatively coupled (e.g., using wired connectionsor wirelessly).

Example embodiments include a method of reducing noise include forming amain signal and one or more reference signals at a beam-former based onat least two received audio signals, detecting voice activity at a voiceactivity detector, where the voice activity detector receives the mainand reference signals and outputting a desired voice activity signal,adaptively cancelling noise at an adaptive noise canceller, where theadaptive noise canceller receives the main, reference, and desired voiceactivity signals and outputs an adaptive noise cancellation signal, andreducing noise at a noise reducer receiving the desired voice activityand adaptive noise cancellation signals and outputting a desired speechsignal.

A further example embodiment of the present invention can include anoise canceling digital signal processor (DSP), including a beam-formerconfigured or communicatively coupled to receive at least two audiosignals and output a main signal and one or more reference signals basedon the at least two audio signals, a voice activity detector configuredor communicatively coupled to receive the main and reference signals andoutput or produce a desired voice activity signal, and adaptive noisecanceller configured or communicatively coupled to receive the main,reference, and desired voice activity signals and to output or producean adaptive noise cancellation signal, and a noise reducer configured orcommunicatively coupled to receive the desired voice activity andadaptive noise cancellation signals and output or produce a desiredspeech signal.

Still further example embodiments of the present invention can include adesired voice activity signal configured or communicatively coupled tocontrol the adaptive noise canceller and the noise reducer. The voiceactivity detector can further include one or more short-time detectors,communicatively coupled to or configured to detect a short-time power ofeach of the received main and reference signals, respectively, one ormore log scalers or amplifiers, communicatively coupled to or configuredto convert the short time power detections (to a logarithmic scale(e.g., in dB) of each short-time detector, respectively, and one or morecombiners, communicatively coupled or configured to receive theamplified short-time power detections of the main signal and one of thereference signals and produce or output a voice activity differencesignal (e.g., in dB) based on the difference between the main andreference signal detections. The short-time detectors may be coupled toreceive a reference or main signal as an input and output the detectedshort-time power to a series amplifier. The short time detectors andamplifiers can be in series for each respective signal. The amplifierscan be logarithmic converters (also referred to as log amplifiers or logscalers). The combiners can combine adjacent signals, such as the mainsignal and one of the at least one reference signals, to produce a voiceactivity difference signal by subtracting the detection(s) of thereference signal from the main signal (or vice-versa).

In still further example embodiments, the voice activity differencesignal can be communicatively coupled to a single signal channel voiceactivity detector, which outputs the desired voice activity signal. Thevoice activity detector can further include one or more OR-gates orAND-gates, the selection of OR-gates or AND-gates based on microphoneconfiguration, arranged to receive multiple desired voice activitysignals and output one of the multiple desired voice activity signalsbased on the OR gate truth (or logic) table. The multiple desired voiceactivity signals can also be final consolidated desired voice activitysignals. The short-time detector may be a root-mean-square (RMS)detector, a power detector, energy detector or similar.

In yet further example embodiments, the beam-former can include one ormore low-pass filters (LPFs) (e.g., de-emphasis filters). The LPFs canbe arranged to filter each of the main and reference signals prior toreception by the voice activity detector. A unitary multi-signal LPF canbe used or individual LPFs for each signal can be used. The LPFs canhave the same frequency response or transfer function characteristics.Alternatively, LPFs may have different frequencies responses andtransfer function characteristics for each signal. The LPFs can have agradual roll-off slope, starting from a frequency between approximately1 kHz and 4 kHz and continuing to the Nyquist frequency. The beam-formercan also include a frequency response matching filter arranged to filterthe reference and/or main signals. The frequency response matchingfilters can be used to adjust the gain, phase, and/or shaping thefrequency response of the signal. The frequency response matchingfilters can be used to match the frequency response of the referenceand/or main signals.

In a yet further example embodiment, a bi-directional pressure-gradientmicrophone elements can provide or output the at least two audio signalsto the VAD module and the channel noise reduction module. Thebi-directional pressure-gradient microphone element can have twoacoustic ports. The pressure-gradient microphone element can be sealedwithin an acoustic housing or acoustic extension or rubber boot such aspolymeric or rubber extensions or boots. The term “seal” or “sealed” asused herein generally refers to an air-tight or hermetic seal. Theacoustic extension can include an acoustic duct for each acoustic port.The acoustic ducts can extend the range of each acoustic port. Thus,near-field talk range of the microphone can be increased. The pressuregradient microphone element, or with the acoustic housing, can befurther mounted airtight within a tube. The tube can be cylindrical,square, or any other shape. The tube can include at least a pair ofacoustic openings and wind-screen material. The acoustic openings can belocated longitudinally along the tube at distances spaced equal to orgreater than the range of each acoustic port. The wind-screen materialcan be a foam or wind-guard material and can be used to fill theinterior of the tube, between the acoustic extension and tube ends. Thecylindrical tube can be a short boom coupled to a headset device.

In still further example embodiments, an array of microphones cangenerate the at least two audio signals. The at least two audio signalscan be received at a beam-former. The audio signals can be digitized.The array of microphones can include at least two pressure gradientmicrophone elements, each pressure gradient microphone element havingtwo acoustic ports. The acoustic ports can be the entry points (inputs)for sound waves. The two pressure gradient microphone elements can bebidirectional and identical. The two pressure gradient microphoneelements can be further sealed within an acoustic housing, acousticextension or airtight rubber boot. The acoustic housing, extension orrubber boot can include an acoustic duct for each acoustic port. Theacoustic ducts can extend the range of each acoustic port. Thus, thenear-field talk range of the microphones can be increased. The pressuregradient microphone elements can further be mounted airtight in serieswithin a substantially cylindrical tube. The cylindrical tube caninclude at least three acoustic openings and wind-screen material orfoam filling material. The acoustic openings can be locatedlongitudinally along the tube at equally spaced distances greater thanthe range of each acoustic duct, or at a range at least equal to therange of each acoustic duct. The wind-screen or foam filling materialcan be used to fill the interior tube space between the acousticopenings and the acoustic ports, thus blocking wind and wind noise. Thewind-screen can be a foam material or other material (e.g., wind guardsleeves over the rubber boots). The cylindrical tube can be a short boomcoupled to a headset device. The cylindrical to can also be coupled to agoose neck desktop microphone device.

In still further embodiments, two omni-directional mics and additionalbeam-forming can be substituted for a pressure gradient microphone withacoustic extension. For example, each pressure gradient microphoneelement can be replaced by two omni-directional microphone elementswhere one omni-directional microphone element is located approximatelyat the position of each acoustic port (at the end of each acousticextension duct). The output or output audio signal produced by the twoomni-directional microphone elements can be received by the beam-formerand processed to produce a beam pattern equivalent to thepressure-gradient microphone beam pattern. The beam-former can be ananalog beam-former or a digital beam-former (that electronically formsbeams). A bi-directional microphone with acoustic port extensions can bereplaced by two omni-directional microphones, each being locatedapproximately at the position of an acoustic port at the end of anacoustic extension duct and additional beam-former circuitry.

In still further example embodiments, the array of microphones can becoupled to a long boom headset device. Such a long boom headset canappear to be a conventional close-talk mic; however, it is a big boommic with two mics in parallel. The end of the microphone boom can bearranged for positioning in front of the user's mouth while remainingmicrophone elements are arranged for positioning at the side(s) of theuser's mouth. The end of the microphone therefore remains a shortdistance from the user's mouth. Such a close talk long boom design canbe used in very heavy noise environments, including military, aviation,and industrial environments. Such a device can provide useful noisecancellation performance. The array of mics can include two pressuregradient noise cancellation microphones, wherein one of the microphonesis positioned directly in front of the mouth of the user, while theother microphone is located at the side of the user's mouth. The twomics can be identical in a single housing (casing) or identicalhousings. The microphone patterns can be directionally parallel to eachother and perpendicular to the boom. Each mic within the housing mightcan have a front and back opening. The digital signal processingcircuitry can be located within the housing between the mics. The arraycan include bi-directional microphones replacing the pressure gradientnoise cancellation microphones. The array can include omni-directionalmicrophones as well. The array can include two to four microphones.

In still further example embodiments, the array of microphones can belocated in-line with a headphone feed connector. The headphone feedconnector can be a pair of ear-buds, such as the type that are typicallyused with a cell phone for hands-free calling, or other similar audioheadset device. Microphones of the array of microphones can be pressuregradient microphones or omni-directional microphones or some othermicrophone type. Such an array of microphones can be located along theconnector (e.g., wire, cable, etc.) at various points, such as close tothe user's mouth or in proximity of the Y split, above, at or below thesplit (the “Y” split is where the left and right ear bud cords splitfrom the input cord connector).

In still further example embodiments, the array of microphones can belocated within or mounted on the housing of an eyeglasses frame. A firstmicrophone can be located near the bridge support (the bridge supportseparates the lenses of the classes and typically sits on or above theuser's nose). The first microphone can have top and bottom acousticports. A second microphone can be located near an end-point of theglasses frames (near a user's temple, between the lens and a supportarm). The second microphone can have top and bottom acoustic ports. Ayet further example embodiment can include a third microphone, locatedat the opposite end-point of the glasses from the second mic and havetop and bottom acoustic ports.

The array of microphones, in a still further embodiment, can includethree or more omni-directional microphone elements. The beam-former canbe further configured to receive an audio signal for each respectivemicrophone element. Thus, there are three or more audio signals input tothe beam-former. The beam-former can include splitters, combiners,amplifiers, and phase shifters. The amplifiers and phase shifters can belocated in series along branches or signals of the beam-forming network,where the splitters and combiners are used to form branches or signalsof the beam-forming network originating from the microphone elements.The beam-former can be further arranged such that adjacent audio signalsare combined to produce two or more audio difference signals. The two ormore audio difference signals can have equivalent phase lengths.

In general, alternate embodiments can be realized by replacing eachbi-directional microphone element with two omni-directional microphoneelements electrically coupled together using a beam-former. Suchsubstitution can achieve an identical beam pattern. In certainembodiments, two bi-directional microphone elements with twoomni-directional elements, alternative embodiments can result bycombining the eliminating one of the two middle positional microphoneelements, such that three microphone elements in series, and adjustingthe beam-forming accordingly. In the three microphone element examplethe middle microphone element is used with beam-forming to produceequivalent beam patterns of both the first bi-directional microphonebeam pattern, forming the main signal, and the second bi-directionalmicrophone beam pattern, forming the reference signal.

Example embodiments of the digital signal processor (DSP) can beimplemented using a system on a chip (SOC), a Bluetooth chip, a DSPchip, or codec with the DSP integrated circuits (ICs).

In a still further example process for reducing noise can be executed ona non-transitory computer program product, including a computer readablemedium having computer readable instructions stored thereon. Thecomputer readable instructions when loaded and executed by a processorcan cause the processor to form beams based on at least two audio signalinputs and produce a main signal and one or more reference signals,detect voice activity based on the main and reference signals andproduce a desired voice activity signal, adaptively cancel noise basedon the main, reference, and desired voice activity signals and producean adaptive noise cancellation signal, and reduce noise based on thedesired voice activity and adaptive noise cancellation signals andoutput a desired speech signal.

Further example embodiments of the present invention may be configuredusing a computer program product; for example, controls may beprogrammed in software for implementing example embodiments of thepresent invention. Further example embodiments of the present inventionmay include a non-transitory computer readable medium containinginstruction that may be executed by a processor, and, when executed,cause the processor to complete methods described herein. It should beunderstood that elements of the block and flow diagrams described hereinmay be implemented in software, hardware, firmware, or other similarimplementation determined in the future. In addition, the elements ofthe block and flow diagrams described herein may be combined or dividedin any manner in software, hardware, or firmware. If implemented insoftware, the software may be written in any language that can supportthe example embodiments disclosed herein. The software may be stored inany form of computer readable medium, such as random access memory(RAM), read only memory (ROM), compact disk read only memory (CD-ROM),“Flash” memory and so forth. In operation, a general purpose orapplication specific processor loads and executes software in a mannerwell understood in the art. It should be understood further that theblock and flow diagrams may include more or fewer elements, be arrangedor oriented differently, or be represented differently. It should beunderstood that implementation may dictate the block, flow, and/ornetwork diagrams and the number of block and flow diagrams illustratingthe execution of embodiments of the invention.

In another embodiment, a handheld device for recording audio includes atop portion and a bottom portion. A first of the array of microphones ishoused in the top portion and a second of the array of microphones is inthe bottom portion. The top portion can also house at least twomicrophones and the bottom portion can house at least two microphones.

In an embodiment, a noise cancelling microphone further includes aheadset, and a short boom housing the noise cancelling microphone. Theshort boom can also house two noise cancelling microphones.

The noise cancelling microphone can also include at least one earphone,the earphone housing the noise cancelling microphone. The noisecancelling microphone can also include eye-glasses configured to houseat least one microphone.

The noise cancelling microphone can also include a headset, the headsetconfigured to house a close-talk dual-microphone long boom.

The noise cancelling microphone can also include a gooseneck podiumconfigured to house at least two microphone elements.

This invention has many advantages. For example, the audio device of theinvention, by virtue of the microphone array, improves accuraterecognition of speech by minimizing unwanted noise, particularly inthose embodiments that employ a digital signal processor that activelycancels unwanted noise, thereby decreasing arrays in such speechrecognition. Further, the present invention integrates the microphonearray and digital signal processor in a convenient and comfortableformat for everyday use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example embodiment of a noisecancellation circuit of the present invention.

FIG. 2 is a block diagram illustrating an example embodiment of abeam-forming module of the invention that can be employed in the noisecancelling circuit.

FIG. 3 is a block diagram illustrating an example embodiment of aDesired Voice Activity Detection Module of the invention.

FIG. 4 is a block diagram illustrating an example embodiment of a noisecancellation circuit of the invention employed to receive a closermicrophone signal and a first and second further microphone signalrespectively.

FIG. 5 is an embodiment of a boom tube housing three microphones in anarrangement of one embodiment of the invention.

FIG. 6 is an embodiment of a boom tube housing four microphones in anarrangement of one embodiment of the invention

FIG. 7 is a block diagram illustrating an example embodiment of abeam-forming module accepting three signals of the invention.

FIG. 8 is a block diagram illustrating an example embodiment of adesired voice activity detection (VAD) module accepting three signals ofthe invention.

FIGS. 9A-B are diagrams illustrating an example embodiment of theinvention including a display and first and second microphones.

FIG. 10 is an illustration of an embodiment of eye-glasses of theinvention having two embedded microphones.

FIG. 11 is an illustration of an embodiment of eyeglasses of theinvention having three embedded microphones.

FIGS. 12A-B are diagrams illustrating an example embodiment of a rubberboot and microphone assembly of the invention.

FIG. 13 is a diagram illustrating example positions of placements of themicrophones of the invention.

FIG. 14 is a block diagram illustrating an example embodiment of a noisecancellation circuit of the present invention employing a singlemicrophone.

FIGS. 15A-15E are diagrams of headsets having a dual-microphoneattached.

FIGS. 16A-B are diagrams illustrating example embodiments of a headsethaving a short boom.

FIGS. 17A-B are diagrams illustrating example embodiments of a headsethaving a short boom.

FIGS. 18A-B are diagrams illustrating example embodiments of two-wayradios.

FIG. 19 is a diagram illustrating an example embodiment of a two-wayradio.

FIG. 20 is a diagram illustrating an example embodiment of a two-wayradio having a microphone in a bottom portion of the device and amicrophone in the top portion of the device.

FIG. 21 is a diagram illustrating an example embodiment of a two-wayradio having four microphones.

FIG. 22 is a diagram of a cellphone includes microphones.

FIG. 23 is a diagram illustrating an example embodiment of a cell phone2302 having four microphones.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

In a head mounted computer, a user can desire a noise-cancelingclose-talk microphone without a boom microphone in front of his or hermouth. The microphone in front of the user's mouth can be viewed asannoying. In addition, moisture from the user's mouth can condense onthe surface of the Electret Condenser Microphone (ECM) membrane, whichafter long usage can deteriorate microphone sensitivity.

In an embodiment, a short tube boom headset can solve these problems byshortening the boom, moving the ECM away from the user's mouth and usinga rubber boot to extend the acoustic port of the noise-cancelingmicrophone. This can extend the effective close-talk range of the ECM.This maintains the noise-canceling ECM property for far away noises. Inaddition, the boom tube can be lined with wind-screen form material.This solution further allows the headset computer to be suitable forenterprise call center, industrial, and general mobile usage. In anembodiment with identical dual-microphones within the tube boom, therespective rubber boots of each microphone can also be identical.

In an embodiment, the short tube boom headset can be a wired or wirelessheadset. The headset includes the short microphone (e.g., and ECM) tubeboom. The tube boom can extend from the housing of the headset along theuser's cheek, where the tube boom is either straight or curved. The tubeboom can extend the length of the cheek to the side of the user's mouth,for instance. The tube boom can include a single noise-cancellingmicrophone on its inside.

The tube boom can further include a dual microphone inside of the tube.A dual microphone can be more effective in cancelling out non-stationarynoise, human noise, music, and high frequency noises. A dual microphonecan be more suitable for mobile communication, speech recognition, or aBluetooth headset. The two microphones can be identical, however aperson of ordinary skill in the art can also design a tube boom havingmicrophones of different models.

In an embodiment having dual-microphones, the two microphones enclosedin their respective rubber boats are placed in series along the insideof the tube.

The tube can have a cylindrical shape, although other shapes arepossible (e.g., a rectangular prism, etc.). The short tube boom can havetwo openings, one at the tip, and a second at the back. The tube surfacecan be covered with a pattern of one or more holes or slits to allowsound to reach the microphone inside the tube boom. In anotherembodiment, the short tube boom can have three openings, one at the tip,another in the middle, and another in the back. The openings can beequally spaced, however, other a person of ordinary skill in the art candesign other spacings.

The microphone in the tube boom is a bi-directional noise-cancellingmicrophone having pressure-gradient microphone elements. The microphonecan be enclosed in a rubber boot extending acoustic port on the frontand the back side of the microphone with acoustic ducts. Inside of theboot, the microphone element is sealed in the air-tight rubber boot.

Within the tube, the microphone with the rubber boot is placed along theinside of the tube. An acoustic port at the tube tip aligns with theboom opening, and an acoustic port at the tube back aligns with boomopening. The rubber boot can be offset from the tube ends to allow forspacing between the tube ends and the rubber boot. The spacing furtherallows breathing room and for room to place a wind-screen of appropriatethickness. The rubber boot and inner wall of the tube remain air-tight,however. A wind-screen foam material (e.g., wind guard sleeves over therubber boot) fills the air-duct and the open space between acoustic portand tube interior/opening.

FIG. 1 is a block diagram 100 illustrating an example embodiment of anoise cancellation circuit of the present invention.

Signals 110 and 112 from two microphones are digitized and fed into thenoise cancelling circuit 101. The noise cancelling circuit 101 can be adigital signal processing (DSP) unit (e.g., software executing on aprocessor, hardware block, or multiple hardware blocks). In anembodiment, the noise cancellation circuit 101 can be a digital signalprocessing (DSP) chip, a system-on-a-chip (SOC), a Bluetooth chip, avoice CODEC with DSP chip, etc. The noise cancellation circuit 101 canbe located in a Bluetooth headset near the user's ear, in an inlinecontrol case with battery, or inside the connector, etc. The noisecancellation circuit 101 can be powered by a battery or by a powersource of the device that the headset is connected to, such as thedevice's batter, or power from a USB, micro-USB, or Lighteningconnector.

The noise cancellation circuit 101 includes four functional blocks: abeam-forming (BF) module 102, a Desired Voice Activity Detection (VAD)Module 108, an adaptive noise cancellation (ANC) module 104 and a singlesignal noise reduction (NR) module 106. The two signals 110 and 112 arefed into the BF module 102, which generates a main signal 130 and areference signal 132 to the ANC module 104. A closer (i.e., relativelyclose to the desired sound) microphone signal 110 is collected from amicrophone closer to the user's mouth and a further (i.e., relativelydistant to the desired sound) microphone signal is collected from amicrophone further from the user's mouth, relatively. The BF module 102also generates a main signal 120 and reference signal 122 for thedesired VAD module 108. The main signal 120 and reference signal 122can, in certain embodiments, be different from the main signal 130 andreference signal 132 generated for the for ANC module 104.

The ANC module 104 processes the main signal 130 and the referencesignal 132 to cancel out noises from the two signals and output a noisecancelled signal 142 to the single channel NR module 106. The singlesignal NR module 106 post-processes the noise cancelled signal 142 fromthe ANC module 104 to remove any further residue noises. Meanwhile, theVAD module 108 derives, from the main signal 120 and reference signal122, a desired voice activity detection (DVAD) signal 140 that indicatesthe presence or absence of speech in the main signal 120 and referencesignal 122. The DVAD signal 140 can then be used to control the ANCmodule 104 and the NR module 106 from the result of BF module 102. TheDVAD signal 140 indicates to the ANC module 104 and the Single ChannelNR module 106 which sections of the signal have voice data to analyze,which can increase the efficiency of processing of the ANC module 104and single channel NR module 106 by ignoring sections of the signalwithout voice data. Desired speech signal 144 is generated by singlechannel NR module 106.

In an embodiment, the BF module 102, ANC module 104, single NR reductionmodule 106, and desired VAD module 108 employ linear processing (e.g.,linear filters). A linear system (which employs linear processing)satisfies the properties of superposition and scaling or homogeneity.The property of superposition means that the output of the system isdirectly proportional to the input. For example, a function F(x) is alinear system if:F(x ₁ +x ₂ +â

)=F(x ₁)+F(x ₂)+â

A satisfies the property of scaling or homogeneity of degree one if theoutput scales proportional to the input. For example, a function F(x)satisfies the properties of scaling or homogeneity if, for a scalar Î±:F(Î±x)=Î±F(x)

In contract, a non-linear function does not satisfy both of theseconditions.

Prior noise cancellation systems employ non-linear processing. By usinglinear processing, increasing the input changes the outputproportionally. However, in non-linear processing, increasing the inputchanges the output non-proportionally. Using linear processing providesan advantage for speech recognition by improving feature extraction.Speaker recognition algorithm is developed based on noiseless voicerecorded in quiet environment with no distortion. A linear noisecancellation algorithm does not introduce nonlinear distortion to noisecancelled speech. Speech recognition can deal with linear distortion onspeech, but not non-linear distortion of speech. Linear noisecancellation algorithm is “transparent” to the speech recognitionengine. Training speech recognition on the variations of nonlineardistorted noise is impossible. Non-linear distortion can disrupt thefeature extraction necessary for speech recognition.

An example of a linear system is a Weiner Filter, which is a linearsingle channel noise removal filter. The Wiener filter is a filter usedto produce an estimate of a desired or target random process by lineartime-invariant filtering an observed noisy process, assuming knownstationary signal, noise spectra, and additive noise. The Wiener filterminimizes the mean square error between the estimated random process andthe desired process.

FIG. 2 is a block diagram 200 illustrating an example embodiment of abeam-forming module 202 that can be employed in the noise cancellingcircuit 101. The BF module 202 receives the closer microphone signal 210and further microphone signal 212.

A further microphone signal 212 is inputted to a frequency responsematching filter 204. The frequency response matching filter 204 adjustsgain, phase, and shapes the frequency response of the further microphonesignal 212. For example, the frequency response matching filter 204 canadjust the signal for the distance between the two microphones, suchthat an outputted reference signal 232 representative of the furthermicrophone signal 212 can be processed with the main signal 230,representative of the closer microphone signal 210. The main signal 230and reference signal 232 are sent to the ANC module.

A closer microphone signal 210 is outputted to the ANC module as a mainsignal 230. The closer microphone signal 210 is also inputted to alow-pass filter 206. The reference signal 232 is inputted to a low-passfilter 208 to create a reference signal 222 sent to the Desired VADmodule. The low-pass filters 206 and 208 adjust the signal for a “closetalk case” by, for example, having a gradual low off from 2 kHz to 4kHz, in one embodiment. Other frequencies can be used for differentdesigns and distances of the microphones to the user's mouth, however.

FIG. 3 is a block diagram illustrating an example embodiment of aDesired Voice Activity Detection Module 302. The DVAD module 302receives a main signal 320 and a reference signal 322 from thebeam-forming module. The main signal 320 and reference signal 322 areprocessed by respective short-time power modules 304 and 306. Theshort-time power modules 304 and 306 can include a root mean square(RMS) detector, a power (PWR) detector, or an energy detector. Theshort-time power modules 304 and 306 output signals to respectiveamplifiers 308 and 310. The amplifiers can be logarithmic converters (orlog/logarithmic amplifiers). The logarithmic converters 308 and 310output to a combiner 312. The combiner 312 is configured to combinesignals, such as the main signal and one of the at least one referencesignals, to produce a voice activity difference signal by subtractingthe detection(s) of the reference signal from the main signal (orvice-versa). The voice activity difference signal is inputted into asingle channel VAD module 314. The single channel VAD module can be aconventional VAD module. The single channel VAD 314 outputs the desiredvoice activity signal.

FIG. 4 is a block diagram 400 illustrating an example embodiment of anoise cancellation circuit 401 employed to receive a closer microphonesignal 410 and a first and second further microphone signal 412 and 414,respectively. The noise cancellation circuit 401 is similar to the noisecancellation circuit 101 described in relation to FIG. 1, however, thenoise cancellation circuit 401 is employed to receive three signalsinstead of two. A beam-forming (BF) module 402 is arranged to receivethe signals 410, 412 and 414 and output a main signal 430, a firstreference signal 432 and second reference signal 434 to an adaptivenoise cancellation module 404. The beam-forming module is furtherconfigured to output a main signal 422, first reference signal 420 andsecond reference signal 424 to a voice activity detection (VAD) module408.

The ANC module 404 produces a noise cancelled signal 442 to a SingleChannel Noise Reduction (NR) module 406, similar to the ANC module 104of FIG. 1. The single NR module 406 then outputs desired speech 444. TheVAD module 408 outputs the DVAD signal to the ANC module 404 and thesingle channel NR module 406.

FIG. 5 is an example embodiment of beam-forming from a boom tube 502housing three microphones 506, 508, and 510. A first microphone 506 isarranged closest to a tip 504 of the boom tube 502, a second microphone508 is arranged in the boom tube 502 further away from the tip 504, anda third microphone 510 is arranged in the boom tube 502 even furtheraway from the tip 504. The first microphone 506 and second microphone508 are arranged to provide data to output a left signal 526. The firstmicrophone is arranged to output its signal to a gain module 512 and adelay module 514, which is outputted to a combiner 522. The secondmicrophone is connected directly to the combiner 522. The combiner 522subtracts the two provided signals to cancel noise, which creates theleft signal 526.

Likewise, the second microphone 508 is connected to a gain module 516and a delay module 518, which is outputted to a combiner 520. The thirdmicrophone 510 is connected directly to the combiner 520. The combiner520 subtracts the two provided signals to cancel noise, which createsthe right signal 520.

FIG. 6 is an example embodiment of beam-forming from a boom tube 652housing four microphones 656, 658, 660 and 662. A first microphone 656is arranged closest to a tip 654 of the boom tube 652, a secondmicrophone 658 is arranged in the boom tube 652 further away from thetip 654, a third microphone 660 is arranged in the boom tube 652 evenfurther away from the tip 654, and a fourth microphone 662 is arrangedin the boom tube 652 away from the tip 654. The first microphone 656 andsecond microphone 658 are arranged to provide data to output a leftsignal 686. The first microphone is arranged to output its signal to again module 672 and a delay module 674, which is outputted to a combiner682. The second microphone is connected directly to the combiner 658.The combiner 682 subtracts the two provided signals to cancel noise,which creates the left signal 686.

Likewise, the third microphone 660 is connected to a gain module 676 anda delay module 678, which is outputted to a combiner 680. The fourthmicrophone 662 is connected directly to the combiner 680. The combiner680 subtracts the two provided signals to cancel noise, which createsthe right signal 684.

FIG. 7 is a block diagram 700 illustrating an example embodiment of abeam-forming module 702 accepting three signals 710, 712 and 714. Acloser microphone signal 710 is output as a main signal 730 to the ANCmodule and also inputted to a low-pass filter 717, to be outputted as amain signal 720 to the VAD module. A first further microphone signal 712and second closer microphone signal 714 are inputted to respectivefrequency response matching filters 706 and 704, the outputs of whichare outputted to be a first reference signal 732 and second referencesignal 734 to the ANC module. The outputs of the frequency responsematching filters 706 and 704 are also outputted to low-pass filters 716and 718, respectively, which output a first reference signal 722 andsecond reference signal 724, respectively.

FIG. 8 is a block diagram 800 illustrating an example embodiment of adesired voice activity detection (VAD) module 802 accepting threesignals 820, 822 and 824. The VAD module 802 receives a main signal 820,a first reference signal 822 and a second reference signal 824 atshort-time power modules 804, 805 and 806, respectively. The short-timepower modules 804, 805, and 806 are similar to the short-time powermodules described in relation to FIG. 3. The short-time power modules804, 805, and 806 output to respective amplifiers 808, 809 and 810,which can each be a logarithmic converter. Amplifiers 808 and 809 outputto a combiner module 811, which subtracts the two signals and outputsthe difference to a single channel VAD module 814. Amplifiers 810 and808 output to a combiner module 812, which subtracts the two signals andoutputs the difference to a single channel VAD module 816. The singlechannel VAD modules 814 and 816 output to a logical OR-gate 818, whichoutputs a DVAD signal 840.

FIG. 9A is a diagram 900 illustrating an example embodiment of a display902 having a first microphone 902 and second microphone 904. The firstmicrophone 902 is arranged to be closer to the user's mouth than thesecond microphone 904, which is further from the user's mouth. In anembodiment, the microphones 902 and 904 are arranged in cylindricalholes in the display's 902 housing.

FIG. 9B is a diagram 950 illustrating an example embodiment of a display952 having a first microphone 952 and second microphone 954. The firstmicrophone 902 is arranged to be closer to the user's mouth than thesecond microphone 954, which is further from the user's mouth. In anembodiment, the microphones 952 and 954 are arranged in cylindricalholes in the display's 952 housing.

FIG. 10 is a diagram 1000 illustrating an example embodiment ofeye-glasses 1002 having embedded microphones. The eye-glasses 1002 havetwo microphones 1004 and 1006, a first microphone 1004 being arranged inthe middle of the eye-glasses 1002 frame and a second microphone 1006being arranged on the side of the eye-glasses 1002 frame. Themicrophones 1004 and 1006 can be pressure-gradient microphone elements,either bi- or uni-directional. Each microphone 1004 and 1006 is within arubber boot. The rubber boot provides an acoustic port on the front andthe back side of the microphone with acoustic ducts. The two microphones1004 and 1006 and their respective boots can be identical. Themicrophone elements 1004 and 1006 can be sealed air-tight (e.g.,hermetically sealed) inside the rubber boots. The acoustic ducts arefilled with wind-screen material. The ports are sealed with woven fabriclayers. The lower and upper acoustic ports are sealed with a water-proofmembrane. The microphones can be built into the structure of the eyeglasses frame. Each microphone has top and bottom holes, being acousticports. In an embodiment, the two microphones 1004 and 1006, which can bepressure-gradient microphone elements, can each be replaced by twoomni-directional microphones.

FIG. 11 is a diagram 1150 illustrating an example embodiment ofeye-glasses 1152 having three embedded microphones. The eye-glasses 1152of FIG. 11 are similar to the eye-glasses 1002 of FIG. 10, but insteademploy three microphones instead of two. The eye-glasses 1152 of FIG. 11have a first microphone 1154 arranged in the middle of the eye-glasses1152, a second microphone 1156 arranged on the left side of theeye-glasses 1152, and a third microphone 1158 arranged on the right sideof the eye-glasses 1152. The three microphones can be employed in thethree-microphone embodiment described above.

FIG. 12A is an exploded view of a microphone assembly 1200 of theinvention. As shown therein, rubber boot 1202 a-b is separated into afirst half of the rubber boot 1202 a and a second half of the rubberboot 1202 b. Microphone 501 is between the rubber boot halves. Eachrubber boot 1202 a-b is lined by a wind-screen 1208 material, howeverFIG. 12A shows the wind-screen in the second half of the rubber boot1202 b. In the case of a pressure-gradient microphone, the air-duct andthe open space between acoustic port and boom interior is filled withwind-screen foam material, such as wind guard sleeves over the rubberboots.

A microphone 1204 is arranged to be played between the two halves of therubber boot 1202 a-b. The microphone 1204 and rubber boot 1202 a-b aresized such that the microphone 1204 fits in a cavity within the halvesof the rubber boot 1202 a-b. The microphone is coupled with a wire 1206,that extends out of the rubber boot 1202 a-b and can be connected to,for instance, the noise cancellation circuit described above.

FIG. 12B is a perspective view of microphone assembly 1200 whenassembled. The rubber boot 1252 of FIG. 12B is shown to have both halves1202 a-b joined together, where a microphone (not shown) is inside. Awire 1256 coupled to the microphone exist the rubber boot 1252 such thatit can be connected to, for instance, the noise cancellation circuitdescribed above.

FIG. 13 is an illustration of an embodiment of the invention 1300showing various optional positions of placement of the microphones 1304a-e. As described above, the microphones are pressure-gradient. In anembodiment, microphones can be placed in any of the locations shown inFIG. 13, or any combination of the locations shown in FIG. 13. In atwo-microphone system, the microphone closest to the user's mouth isreferred to as MIC1, the microphone further from the user's mouth isreferred to as MIC2. In an embodiment, both MIC1 & MIC2 can be inline atposition 1 1304 a. In other embodiments, the microphones can bepositioned as follows:

-   -   MIC1 at position 1 1304 a and MIC2 at position 2 1304 b;    -   MIC1 at position 1 1304 a and MIC2 at position 3 1304 c;    -   MIC1 at position 1 1304 a and MIC2 at position 4 1304 d;    -   MIC1 at position 4 1304 d and MIC2 at position 5 1304 e;    -   Both MIC1 and MIC2 at position 4 1304 d.

If position 4 1304 d has a microphone, it is employed within a pendant.

The microphones can also be employed at other combinations of positions1304 a-e, or at positions not shown in FIG. 13.

Each pressure-gradient microphone element can be replaced with twoomni-directional microphones at the location of each acoustic port,resulting in four total microphones. The signal from these twoomni-directional microphone can be processed by electronic or digitalbeam-forming circuitry described above to produce a pressure gradientbeam pattern. This pressure gradient beam pattern replaces theequivalent pressure-gradient microphone.

In an embodiment of the present invention, if a pressure-gradientmicrophone is employed, each microphone is within a rubber boot thatextends an acoustic port on the front and the back side of themicrophone with acoustic ducts. At the end of rubber boot, the newacoustic port is aligned with the opening in the tube, where empty spaceis filled with wind-screen material. If two omni-directional microphonesare employed in place of one pressure-gradient microphone, then theacoustic port of each microphone is aligned with the opening.

In an embodiment, a long boom dual-microphone headset can look like aconventional close-talk boom microphone, but is a big boom withtwo-microphones in parallel. An end microphone of the boom is placed infront of user's mouth. The close-talk long boom dual-microphone designtargets heavy noise usage in military, aviation, industrial and hasunparalleled noise cancellation performance. For example, one mainmicrophone can be positioned directly in front of mouth. A secondmicrophone can be positioned at the side of the mouth. The twomicrophones can be identical with identical casing. The two microphonescan be placed in parallel, perpendicular to the boom. Each microphonehas front and back openings. DSP circuitry can be in the housing betweenthe two microphones.

Microphone is housed in a rubber or silicon holder (e.g., the rubberboot) with an air duct extending to the acoustic ports as needed. Thehousing keeps the microphone in an air-tight container and providesshock absorption. The microphone front and back ports are covered with awind-screen layer made of woven fabric layers to reduce wind noise orwind-screen foam material. The outlet holes on the microphone plastichousing can be covered with water-resistant thin film material orspecial water-resistant coating.

In another embodiment, a conference gooseneck microphone can providenoise cancellation. In large conference hall, echoes can be a problemfor sound recording. Echoes recorded by a microphone can cause howling.Severe echo prevents the user from tuning up speaker volume and causeslimited audibility. Conference hall and conference room can be decoratedwith expensive sound absorbing materials on their walls to reduce echoto achieve higher speaker volume and provide an even distribution ofsound field across the entire audience. Electronic echo cancellationequipment is used to reduce echo and increase speaker volume, but suchequipment is expensive, can be difficult to setup and often requires anacoustic expert.

In an embodiment, a dual-microphone noise cancellation conferencemicrophone can provide an inexpensive, easy to implement solution to theproblem of echo in a conference hall or conference room. Thedual-microphone system described above can be placed in a desktopgooseneck microphone. Each microphone in the tube is a pressure-gradientbi-directional, uni-directional, or super-directional microphone.

FIG. 14 is a block diagram 1400 illustrating an example embodiment of anoise cancellation circuit of the present invention employing a singlemicrophone. A single microphone signal 1402 is received at an activitydetection module (VAD) 1404 and a single channel noise reduction module(NR) 1406. The activity detection module (VAD) 1404 determines thesignal microphone signal 1402 contains speech, and notifies the singlechannel noise reduction module (NR) 1406. The single channel noisereduction module (NR) 1406, responsive to the signal from the activitydetection module (VD) 1404, reduces noise on the single microphonesignal 1402 and outputs desired speech 1408.

FIG. 15 is a diagram 1500 of a headset 1502 having a dual-microphone1503 attached. The dual-microphones 1503 are contained in a housing, butthe individual microphones within the housing are shown by pictures ofmicrophone 1504 and 1506.

FIG. 16 is a diagram 1600 illustrating an example embodiment of aheadset 1602 having a short boom 1604. The short boom 1604 houses asingle microphone 1606 which is enclosed in a rubber boot, describedherein above.

FIG. 17 is a diagram 1700 illustrating an example embodiment of aheadset 1702 having a short boom 1704. The short boom 1704 houses dualmicrophones 1706, comprised of microphone 1706 a and 1706 b. Bothmicrophones 1706 a-b are enclosed in a rubber boot, described hereinabove.

FIG. 18 is a diagram 1800 illustrating example embodiments of two-wayradios 1802 and 1804. Two-way radios are widely used for public safety,enterprise and industrial applications, and consumer applications.

FIG. 19 is a diagram 1900 illustrating an example embodiment of atwo-way radio 1902. The two-way radio includes a microphone 1904 in abottom portion of the two-way radio 1902 and a microphone 1906 in a topportion of the two-way radio 1902. Traditionally, a two-way radio onlyhas a microphone in the top part of the device. In an embodiment of thepresent invention, a second microphone is employed at the bottom of thetwo-way radio 1902 to provide a main microphone at the top and areference microphone at the bottom. The user employs a push-to-talkbutton or feature near the top of the device.

FIG. 20 is a diagram 2000 illustrating an example embodiment of atwo-way radio 2002 having a microphone 2004 in a bottom portion of thedevice and a microphone 2006 in the top portion of the device. Themicrophones 2004 and 2006 can be bi-directional microphones with anacoustic extension to the ports in the front and back case surface ofthe device.

FIG. 21 is a diagram 2100 illustrating an example embodiment of atwo-way radio 2100 having four microphones. The two-way radio 2102 hastwo microphones 2104 and 2106 in the bottom portion and two microphones2108 and 2110 in the top portion. Each bi-directional microphone with anextension shown in previous embodiments can be replaced with twoomni-directional microphones (e.g., microphones 2104 and 2106 andmicrophones 2108 and 2110) at each port. The four omni-directionalmicrophone configuration can occupy less space and therefore fit into asmaller device. The omni-directional microphone can be a MEMSmicrophone. Four microphone is more flexible for speech recorded fromfurther away. The two microphones of the top portion can electronicallyform a uni-directional beam for far field talk or video recording.

FIG. 22 is a diagram 2200 of a cellphone 2202 includes microphones 2204and 2206. Handheld smartphones traditionally have a microphone on thebottom part of the phone. The user talks closely to the bottom part ofthe device while holding it. The same bi-directional microphone with anacoustic extension to the ports can be in the front and back casesurface of the device. The main microphone can be in the bottom portionof the cell phone 2202 and reference microphone can be at the topportion.

FIG. 23 is a diagram 2300 illustrating an example embodiment of a cellphone 2302 having four microphones. Each bi-directional microphone withextension can be replaced with two omni-directional microphones at eachport location. The four omni-directional microphone configuration canfit into a smaller device and therefore occupy less space. Theomni-directional microphone can be a MEMS microphone. Four-microphonescan be more flexible for a far talk scenario. Upper two microphones canelectronically form a uni-directional beam for far field talk or videorecording.

The relevant teachings of all patents, published applications andreferences cited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A noise cancelling digital signal processor(DSP), comprising: a) a beam-forming module configured to output a mainsignal and one or more reference signals based on audio signals receivedfrom at least two microphones, wherein the beam-forming module includesone or more de-emphasis filters, each of which comprises at least one ofa low-pass filter and a frequency response matching filter, each of theone or more de-emphasis filters arranged to filter at least one of themain and reference signals; b) a voice activity detection moduleconfigured to receive the main signal and reference signals and tooutput a desired voice activity signal, and whereby a first one of theone or more de-emphasis filters is arranged to filter the main signal,and a second one of the one or more de-emphasis filters is arranged tofilter the reference signal, prior to reception of the main signal andthe reference signal by the voice activity detection module; c) anadaptive noise cancellation module configured to receive the mainsignal, reference signals and desired voice activity signal and outputan adaptive noise cancelled signal; and d) a single channel noisereduction module configured to receive the desired voice activity signaland adaptive noise cancellation signal and output a desired speechsignal.
 2. The noise cancelling DSP of claim 1, wherein the desiredvoice activity signal is further configured to control the adaptivenoise cancellation module and the noise reduction module.
 3. The noisecancelling DSP of claim 1, wherein the voice activity detection modulefurther includes: a) one or more short-time detectors, configured todetect a short-time power of each of the received main and referencesignals, respectively; b) one or more log scalers, configured to convertthe detected short-time power of each short-time detector, respectively;and c) one or more combiners, configured to receive the log scaledshort-time power detections of the main signal and one of the referencesignals and produce a voice activity difference signal based on saiddetections.
 4. The noise cancelling DSP of claim 3, wherein the voiceactivity difference signal is further communicatively coupled to asignal channel voice activity detection module outputting the desiredvoice activity signal.
 5. The noise cancelling DSP of claim 4, whereinthe voice activity detection module further includes an OR-gate or anAND-gate, based on microphone configuration, arranged to receivemultiple desired voice activity signals and output one of the multipledesired voice activity signals.
 6. The noise cancelling DSP of claim 3,wherein the short-time detector is a root-mean-square detector, powerdetector, or energy detector.
 7. The noise cancelling DSP of claim 1,wherein the low-pass filter adjusts at least one of the main signal andthe reference signal to accommodate a close talk range of the at leasttwo microphones.
 8. The noise cancelling DSP of claim 7, wherein thede-emphasis filter has a gradual slope roll-off starting at a frequencyapproximately between 1 kHz and 4 kHz and continuing to approximately aNyquist frequency.